When making measurements of electrical activity in the human body, such as for Electroencephalography (EEG), Electrocardiography (ECG), Electromyography (EMG), Evoked Potentials (EPs), Electronystagmography (ENG), and/or other electrophysiologic potentials, there are several types of electrodes that are commonly used. Surface electrodes can be attached to the surface of the patient's skin using adhesives such as glue or using tape or staples. In order to make good electrical contact, a conductive gel or paste is often used between the electrode and the skin. Surface electrodes, however suffer from a number of disadvantages. The conductive gel used can, over time, dry out or otherwise degrade so as to change the effective impedance value. This is especially true during long procedures such as a surgery lasting as long as six hours or more. Surface electrodes can also dislodge, when glue and/or tape is used. If staples are used then there is an associated tissue injury, pain, and risk of infection. Some glue adhesives are flammable and may be incompatible with application in an operating room. In some cases, such as when placing electrodes on skin with hair or on the scalp, an abrasion is made to remove dead skin cells and reduce impedance. However, such abrasion can cause further discomfort to the patient as well as add time to the process.
Subdermal electrodes, such as needle electrodes are sometimes used, to alleviate some of the drawbacks associated with surface electrodes. In particular, subdermal needle electrodes avoid the use of adhesive glues, abrasions prior to placement, and the use of conductive gels or pastes that can raise impedance over time. Needle electrodes can also be easier to place, thereby lessening the time needed to set up the procedure. However needle type subdermal electrodes have drawbacks as well. A primary concern is for the safety of the medical personnel, such as doctors, nurses, technologist, and other personnel that can be inadvertently injured by the needle electrode after it is removed from the patient. These sharps injuries expose the personnel to bloodborne pathogens that are present in human blood and can cause disease in humans. Examples of such pathogens includes Human Immunodeficiency Virus (HIV), Hepatitis B Virus (HBV), and Hepatitis C Virus (HCV). Other drawbacks of needle type subdermal electrodes include stabilization of the electrode when positioned on the patient. Needle electrodes can be taped in place but tape is typically insufficient to secure the electrode. Staples can be used, but they present an additional sharps hazard and associated infection risk.